Hydraulically actuated braking system for unitary control of driven and towed vehicles

ABSTRACT

A hydraulically actuated braking system to enable the interconnecting of a driven and a towed vehicle, whereby the hydraulic fluid conduit of the driven vehicle is connected in fluid communication to a cylinder-plunger assembly by a flexible conduit, which cylinder-plunger assembly may be connected in end to end relation with an auxiliary master cylinder mounted on the towed vehicle. The auxiliary master cylinder is connected in fluid communication with the hydraulic fluid conduit system which leads to the brakes of the towed vehicle, and, by closing a valve intermediate the conduit system and the normal master cylinder of the towed vehicle, and opening a valve in a conduit intermediate the auxiliary master cylinder and the hydraulic fluid conduit system of the towed vehicle, mechanical force may be applied by the plunger of the hydraulic fluid cylinder-plunger assembly to the auxiliary master cylinder. The cylinder-plunger assembly is connected in fluid communication with the hydraulic fluid brake system of the driven vehicle, and the driven vehicle and the towed vehicle may be accurately controlled simultaneously by the application of the brake pedal of the driven vehicle. Provision is made to close a valve in a conduit intermediate the auxiliary cylinder and the conduit system of the towed vehicle, and opening a valve in the conduit leading from the original master cylinder to the conduit system of the towed vehicle, to enable the towed vehicle to be used in the same manner as if the auxiliary hydraulic cylinder arrangement was not installed thereon. It is to be pointed out that the separation of the hydraulic cylinderplunger assembly from the auxiliary master cylinder may be accomplished without loss of hydraulic fluid.

United States Patent Meeks [451 Mar. 21, 1972 [54] HYDRAULICALLYACTUATED BRAKING SYSTEM FOR UNITARY CONTROL OF DRIVEN AND TOWED VEHICLES[72] Inventor: Walter Melvin Meeks, Henrietta, Tex.

[73] Assignees: Wayland D. Keith; Leverne E. Mangel,

Wichita Falls, Tex.

22 Filed: Jan. 12,1970

[21] Appl.No.: 2,044

[51] Int. Cl. ..B60t 7/00 [58] Field of Search ..303/7, 48-49; 280/420,421; 180/14; 188/112, 3

Primary Examiner-Milton Buchler Assistant Examiner.lohn J. McLaughlinAttorney-Wayland D. Keith [57 I ABSTRACT A hydraulically actuatedbraking system to enable the interconnecting of a driven and a towedvehicle, whereby the hydraulic fluid conduit of the driven vehicle isconnected in fluid communication to a cylinder-plunger assembly by aflexible conduit, which cylinder-plunger assembly may be connected inend to end relation with an auxiliary master cylinder mounted on thetowed vehicle. The auxiliary master cylinder is connected in fluidcommunication with the hydraulic fluid conduit system which leads to thebrakes of the towed vehicle, and, by closing a valve intermediate theconduit system and the normal master cylinder of the towed vehicle, andopening a valve in a conduit intermediate the auxiliary master cylinderand the hydraulic fluid conduit system of the towed vehicle, mechanicalforce may be applied by the plunger of the hydraulic fluidcylinder-plunger assembly to the auxiliary master cylinder. Thecylinder-plunger assembly is connected in fluid communication with thehydraulic fluid brake system of the driven vehicle, and the drivenvehicle and the towed vehicle may be accurately controlledsimultaneously by the application of the brake pedal of the drivenvehicle. Provision is made to close a valve in a conduit intermediatethe auxiliary cylinder and the conduit system of the towed vehicle, andopening a valve in the conduit leading from the original master cylinderto the conduit system of the towed vehicle, to enable the towed vehicleto be used in the same manner as if the auxiliary hydraulic cylinderarrangement was not installed thereon. It is to be pointed out that theseparation of the hydraulic cylinder-plunger assembly from the auxiliarymaster cylinder may be accomplished without loss of hydraulic fluid.

8 Claims, 4 Drawing Figures Patented March 21, 1972 WALTER MELVIN MEEKSJNVENTOR.

BY M1151 HISAGENT' HYDRAULICALLY ACTUATED BRAKING SYSTEM FOR UNITARYCONTROL OF DRIVEN AND TOWED VEHICLES This invention relates toimprovements in hydraulic brake systems and more particularly to ahydraulic brake system which enables a driven vehicle to tow a vehicleand control the braking sensitivity of both vehicles without having tomanually actuate mechanism on the driven vehicle, except the normalbrake pedal.

The present device is so constructed that the hydraulic systems of thedriven vehicle and the towed vehicle may be disconnected without theloss of fluid from either system, and which disconnection can be done ina minimum of time, with each hydraulic braking system being placed incondition, in a few minutes time, to operate independently of the other,without impairing the original effectiveness of either brake system.

Various fluid actuated braking systems have been proposed heretofore,but these, in so far as known, separated live fluid lines, and even withautomatic checks within the lines, some fluid was allowed to escape, andfurthermore, the parted lines were subject to contamination by foreignmatter, such as dirt and mud or the like.

The present invention is so constructed as to provide a separatehydraulically actuated master cylinder, which is connected with thehydraulic braking system of the towed vehicle, which master cylinder isactuated by a hydraulic cylinderplunger assembly connected to thehydraulic system of the driven vehicle.

An object of this invention is to provide a hydraulic system for adriven vehicle to actuate a mechanism which actuates a hydraulic systemof a towed vehicle, which hydraulic systems are not connected in fluidcommunication.

Another object of the invention is to provide a hydraulic system for adriven vehicle which may be quickly disconnected from the hydraulicsystem of a towed vehicle, without the loss of fluid.

Still another object of the invention is to provide a hydraulic systemfor a driven vehicle which may be mechanically connected to thehydraulic system of a towed vehicle in such manner that the twohydraulic braking systems may be separated and used independently, andstill be as effective as originally designed.

A further object of the invention is to provide an auxiliary mastercylinder for the towed vehicle, which cylinder is mechanically actuatedby a hydraulic cylinder-plunger arrangement, and which system may beleft on the towed vehicle, and can be de-energized by closing one valvein the hydraulic braking system of the towed vehicle and opening anothervalve in the hydraulic braking system thereof to effectively place theoriginal hydraulic braking system of the towed vehicle in operativecondition.

With these objects in mind and others which will become manifest as thedescription proceeds, reference is to be had to the accompanyingdrawings in which like reference characters designate like parts in theseveral views thereof, in which:

FIG. 1 is a diagrammatic view of the chassis of a driven vehicle and ofa towed vehicle, showing the hydraulic systems thereof diagrammatically,showing the towed vehicle connected to the driven vehicle by a tow bar,and showing the hydraulic systems as being mechanically interconnected;

FIG. 2 is an enlarged, longitudinal sectional view through a mastercylinder of the towed vehicle, showing the hydraulic cylinder-plungerassembly connected thereto for mechanical actuation by a hydraulicplunger;

FIG. 3 is an enlarged, fragmentary sectional view similar to FIG. 2 butshowing the hydraulic cylinder-plunger assembly,

of the towed vehicle, in disconnected relation with respect to theauxiliary master cylinder of the towed vehicle;

FIG. 4 is an enlarged sectional view taken on the line 4--4 of FIG. 1,looking in the direction indicated by the arrows.

With more detailed reference to the drawing, the numeral 1 designatesgenerally a driven vehicle and the numeral 2 designates generally atowed vehicle. The driven vehicle 1 has a trailer hitch 4 connectedthereto in a conventional manner, which trailer hitch usually has aconnection means thereon, such as a ball, pin, or the like, to connectwith the tow bar 6, which tow bar is usually hingeably connected to thetowed vehicle 2 by a pin' 8. FIG. 1 shows the driven vehicle and thetowed vehicle connected in towed relation.

The driven vehicle has a .hydraulic braking system with a mastercylinder 10, which cylinder is actuated by a pedal 12 or the like, whichdirects hydraulic fluid under pressure into a hydraulic conduit system14, which conduit system leads to hydraulic brakes (not shown) connectedto each of the wheels 16. The hydraulic system is consideredconventional and is well known in the art, therefore it is notconsidered necessary to illustrate such system in detail. Upondepressing brake pedal 12, hydraulic fluid will flow into conduit system14 and to each of the wheels 16, and upon release of brake pedal 12, thehydraulic fluid will be released from the respective brake cylinders(not shown) in the wheels 16, and the hydraulic fluid will return to thehydraulic master cylinder 10 in a manner well known in the art ofhydraulic brakes. The hydraulic system of the towed vehicle 2 is shownto be substantially identical with the hydraulic conduit system 14 ofthe driven vehicle, for simplicity of illustration and for simplicity ofdescription and understanding. The numerals as applied to the towedvehicle 2 will be the same as the numerals applied to the driven vehicle1, except the elements will have a sufiix T thereto to designate thetowed vehicle system, in so far as applicable. The primary mastercylinder of the towed vehicle is indicated at 10T and has a brake pedal12T to normally operate the mechanism therein. The hydraulic conduitsystem of the towed vehicle is designated 141 and leads to the brakes ofthe respective wheels 16T.

The towed vehicle has an auxiliary master cylinder by the numeral 20,which auxiliary cylinder is mounted on a bifurcated bracket 22 which issecured to the bumper 23 of the towed vehicle 2. The master cylinder 20is bolted to the bifurcated bracket 22 by bolts 24, which bolts passthrough bracket 22, flange 26 and flange 28 to bindingly engage ahydraulic cylinder-plunger assembly 30 in binding engagement with theend of the auxiliary master cylinder 20. t

The auxiliary master cylinder 20 has a plunger 32 therein, which plungeris actuated within the bore 34 of the master cylinder by a plunger 36,which is associated with a piston 38 within cylinder-plunger assembly30. The plunger 36 may be attached to the piston 38 and have the endthereof in bearing relation within a cup 40 in the outer end ofauxiliary master cylinder piston 32. Conventional cups or fluid seals 42and 44 are provided on auxiliary master cylinder piston 32 and a cup orfluid seal 46 is provided on piston 38 so as to prevent leakage ofhydraulic fluid from the respective systems. Removable cylinder heads 48and 50 may be provided in the bore 34 of the auxiliary master cylinder20 and the bore 52 of hydraulic cylinder-plunger assembly 30. Therespective cylinder heads 48 and 50 are preferably maintained in placeby the respective snap rings 54 and 56. Each of the cylinder heads 48and 50 is provided with the respective wiper seals 58 and 60 to maintainthe cylinders free of foreign matter. A relatively strong spring 62 isprovided within the bore 34 of auxiliary master cylinder 20 between cup42 and the end of the cylinder to which the fluid conduit is connected.A relatively weak spring 64 is provided in cylinder 52 intermediate thecup 46 and the end of the cylinder to which the fluid conduit isconnected. With the springs 62 and 64 in this relation, the spring 62will normally keep the piston 32 in the position shown in FIG. 2, exceptwhen the brake of the driven vehicle is being used, and the weakerspring 64 will normally be compressed.

With the master cylinder 20 and the hydraulic cylinderplunger assemblyin this relation, a tee 66 is installed within the hydraulic conduitsystem 14 to which a conduit coupling 68 connects to a flexible conduit70 in a conventional manner, and to a conduit connection 72 on conduit74 which leads to the end of cylinder-plunger assembly 30. A conduit 76leads from the opposite end of auxiliary master cylinder 20 to that towhich the cylinder-plunger assembly is connected, and through a cut-offvalve 78 and into a tee 80 within hydraulic conduit system 14T of thetowed vehicle 2. A valve 82 is within the conduit which interconnectsthe master cylinder lOT with conduit system 14T of the towed vehicle, sowhen the valve 82 is closed the master cylinder T is renderedinoperative, and with the valve 78 open, the auxiliary hydrauliccylinder 20 is rendered operative and with the reservoir 21 of theauxiliary master cylinder 20 filled with hydraulic fluid, this mastercylinder will function upon movement of master cylinder-plunger 32 bythe action of plunger 36. A pressure switch 84 is connected in fluidcommunication with the auxiliary master cylinder 20 to function in thesame manner as the pressure switch on master cylinders 10 and 10T, andwith the circuit 86 connected in parallel with the circuit leading tothe stop light (not shown) on the towed vehicle, the stop light willfunction in the proper manner upon the application of brake pedal 12.

OPERATION In order to tow a vehicle 2 behind a driven vehicle 1, thetowed vehicle 2 is connected to the trailer hitch 4 by tow bar 6. Toconnect the auxiliary master cylinder 20 and the plunger-cylinderassembly 30, bolts 24 connect to the respective flanges 26 and 28, inthe manner shown in FIG. 2. Before the vehicles are connected, thehydraulic cylinder-plunger as sembly 30 will have the plunger 36extended and the piston 38 will be seated against piston head 50, whichis held against outward movement by snap ring 56, due to the pressureexerted by weak spring 64, which will keep the piston sealed againstentrance of water, dirt or other foreign matter. The strong spring 62will keep the piston 32 at the opposite end of bore 32 from the end towhich the conduit 76 is connectedv With the bolts 24 securing thebracket 22, flange 26 and flange 28 in place, the device is ready tooperate. By closing valve 82, between conduit system MT and mastercylinder 10T, and opening valve 78, between auxiliary master cylinder 20and conduit system 14T of the towed vehicle, the brake pedal 12 may beapplied which will direct hydraulic fluid from master cylinder 10 tonormally apply pressure to each of the brakes in wheels 16. Fluid willalso be directed through tee 66, conduits 70 and 74 into hydrauliccylinder-plunger assembly 30 to urge the plunger 36 outward againstauxiliary master cylinder piston 32 to compress spring 62 and dischargehydraulic fluid into conduit 76 which leads through open valve 78, andwith valve 82 closed, the hydraulic fluid will be directed into conduitsystem 14T leading to the brakes of the towed vehicle. With the valve 82closed, the sensitivity of the brakes on each of the vehicles is uniformand the braking of the wheels is controlled by a single brake pedal 12,with perfect uniformity.

When it is desired to operate the vehicles separately the bolts 24 areremoved in order to disconnect flanges 26 and 28 in the manner shown inFIG. 3. The bolts 24 may be used to bolt flange 26 to bifurcated bracket22, then by closing valve 78 and opening valve 82, the hydraulic brakeconduit system 14T may be controlled by pedal 12T and master cylinder10T on vehicle 2. Upon disconnecting the tow bar 6 from trailer hitch 4and moving the hydraulic cylinder-plunger assembly 30 to a position onthe driven vehicle 1, it may rest there without disconnecting the fluidconduit therefrom. The brake on the driven vehicle may be operated bypedal 12 to operate the master cylinder 10 to direct hydraulic fluidinto hydraulic brake system 14 and with the piston 38 resting againstcylinder head 50, which is retained in place by snap ring 56, thehydraulic braking system of the driven vehicle 1 will function normally,and without loss of fluid. If desired, the plunger 36 may be a looselypositioned plunger, which may be removed without removing piston 38,when the cylinder-plunger assembly 30 is disconnected from the auxiliarymaster cylinder 20.

Having thus clearly shown and described the invention, what is claimedas new and desired to be secured by Letters Patent is:

1. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled for movement over the terrainunder the power of the driven vehicle, which braking system comprises;

a. a first hydraulic braking system mounted on the driven vehicle, whichbraking system includes a master cylinder,

a conduit system leading to the respective brakes of the driven vehicle,and a further conduit which connects the master cylinder with saidconduit system leading to the brakes thereof,

1. said master cylinder of the driven vehicle being manually operated,

b. a second hydraulic braking system associated with th towed vehicle,which braking system includes a master cylinder, a conduit systemleading to the respective brakes of the towed vehicle, and a conduitconnecting the master cylinder of the towed vehicle with the conduitsystem leading to the brakes thereof,

1. a valve within said conduit connecting the master cylinder of thetowed vehicle to the conduit system leading to the respective brakesthereof,

0. an auxiliary master cylinder, including a piston, mounted on thetowed vehicle,

1. a conduit connected in fluid communication with said auxiliary mastercylinder and with said conduit system leading to the brakes of the towedvehicle, 7

2. a valve within said conduit which interconnects said auxiliary mastercylinder with the hydraulic braking system of the towed vehicle,

d. a hydraulic conduit connected in fluid communication with the conduitsystem leading to the respective brakes of the driven vehicle, l. ahydraulic cylinder-plunger assembly operatively connected, in fluidcommunication, with said conduit leading from said conduit system ofsaid driven vehicle,

e. mechanical means interconnecting said hydraulic cylinder-plungerassembly with said auxiliary master cylinder so the plunger of saidhydraulic cylinder-plunger assembly will mechanically actuate the pistonof said auxiliary master cylinder, so, upon operation of said manuallycontrolled master cylinder on said driven vehicle, said auxiliary mastercylinder will transmit fluid under pressure to the brakes of thehydraulic braking system of the towed vehicle to simultaneously engagethe brakes on the towed vehicle and the brakes on the driven vehicle.

2. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled for movement over the terrain,under the power of the driven vehicle, as defined in claim 1; wherein a.said hydraulic conduit which is connected in fluid communication withthe conduit system leading to the respective brakes of the drivenvehicle, is a flexible conduit.

3. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled for movement over the terrain,as defined in claim 2; wherein a. said cylinder-plunger assemblyconnected to said flexible conduit is connected in axial alignment withthe piston of said auxiliary master cylinder.

4. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are coupled for movement over the terrain; as deflned inclaim 3, wherein a. fastening means detachably secure saidcylinder-plunger assembly to said auxiliary master cylinder.

5. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled for movement over the terrainunder the power of the driven vehicle, as defined in claim 1; wherein a.said valve means interposed between said master cylinder on the towedvehicle and the conduit system leading to the respective brakes thereofis adapted to be selectively closed, and

b. said valve within said conduit which interconnects said auxiliarymaster cylinder and the hydraulic braking system of the towed vehicle isadapted to be opened to render the hydraulic braking system of the towedvehicle simultaneously operable with the braking system of the drivenvehicle.

6. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled-for movement over the terrainunder the power ofthe driven vehicle, as defined in claim 1; wherein a.said cylinder-plunger assembly having the piston fitted therein in fluidtight relation,

1. stop means limiting the outward movement of said piston,

b. the piston of said auxiliary master cylinder being in fluid tightsealing relation with the cylinder thereof,

1, stop means limiting the outward movement of said piston,

c. mechanical means disconnecting the hydraulic cylinderplunger assemblyfrom said auxiliary master cylinder so the hydraulic cylinderplungerassembly may be maintained with the driven vehicle and the auxiliarymaster cylinder may be retained with the towed vehicle without loss ofhydraulic fluid from either system, to enable the use of the brakingsystem of the driven vehicle and of the towed vehicle independently,when the vehicles are mechanically disconnected.

7. An apparatus embodying two hydraulic systems, which systems areadapted to be mechanically connected so one of the systems issynchronously operated by the other of said systems without thehydraulic fluid from one system passing into the other of the hydraulicsystems, which apparatus comprises;

a. a first master hydraulic power cylinder,

b. a first conduit system connected in fluid communication with saidfirst master hydraulic power cylinder and leading therefrom,

c. a first hydraulic power actuated cylinder-plunger as semblyoperatively connected in fluid communication with said first conduitsystem,

d. a second master hydraulic power cylinder,

1. a second conduit system connected in fluid communication with saidsecond .master hydraulic power cylinder and leading therefrom,

e. a second hydraulic power actuated cylinder-plunger assemblyoperatively connected, in fluid communication, with said second conduitsystem,

f. an auxiliary master hydraulic power cylinder,

1. said second conduit system being connected in fluid communicationwith said auxiliary master hydraulic cylinder,

2. selectively controlable valve means intermediate said auxiliarymaster hydraulic power cylinder and said con duit system leading to saidsecond hydraulic power actuated cylinder-plunger assembly,

g. selectively controllable valve means intermediate said second masterhydraulic power cylinder and said second conduit system leading to saidsecond hydraulic power actuated cylinder-plunger assembly,

h. said plunger extending from said first hydraulic power actuatedcylinder-plunger assembly and being connected, in power transmittingrelation with said auxiliary master hydraulic power cylinder, so uponactuation of said first master hydraulic power cylinder, said plunger ofsaid first hydraulic power actuated cylinder will actuate said auxiliarymaster hydraulic power cylinder, which, in turn, will actuate saidsecond hydraulic power actuated c'ylinder,

. said first power actuated cylinder being separable with respect tosaid auxiliary master hydraulic power cylinder so no loss of hydraulicfluid will be had when the two systems are separated, and

j. fastening means detachably connecting said first hydraulic poweractuated cylinder-plunger assembly with said auxiliary master hydraulicpower cylinder to transmit lineal force to said auxiliarg masterhydraulic power cylinder.

An apparatus em odying two hydraulic systems, as

defined in claim 7, wherein a. said second hydraulic system has aplurality of cylinderplunger assemblies operatively connected in fluidcommunication with said second conduit system.

1. A hydraulic braking system for a driven vehicle and a towed vehicle,which vehicles are mechanically coupled for movement over the terrainunder the power of the driven vehicle, which braking system comprises;a. a first hydraulic braking system mounted on the driven vehicle, whichbraking system includes a master cylinder, a conduit system leading tothe respective brakes of the driven vehicle, and a further conduit whichconnects the master cylinder with said conduit system leading to thebrakes thereof,
 1. said master cylinder of the driven vehicle beingmanually operated, b. a second hydraulic braking system associated withthe towed vehicle, which braking system includes a master cylinder, aconduit system leading to the respective brakes of the towed vehicle,and a conduit connecting the master cylinder of the towed vehicle withthe conduit system leading to the brakes thereof,
 1. a valve within saidconduit connecting the master cylinder of the towed vehicle to theconduit system leading tO the respective brakes thereof, c. an auxiliarymaster cylinder, including a piston, mounted on the towed vehicle,
 1. aconduit connected in fluid communication with said auxiliary mastercylinder and with said conduit system leading to the brakes of the towedvehicle,
 2. a valve within said conduit which interconnects saidauxiliary master cylinder with the hydraulic braking system of the towedvehicle, d. a hydraulic conduit connected in fluid communication withthe conduit system leading to the respective brakes of the drivenvehicle,
 1. a hydraulic cylinder-plunger assembly operatively connected,in fluid communication, with said conduit leading from said conduitsystem of said driven vehicle, e. mechanical means interconnecting saidhydraulic cylinderplunger assembly with said auxiliary master cylinderso the plunger of said hydraulic cylinder-plunger assembly willmechanically actuate the piston of said auxiliary master cylinder, so,upon operation of said manually controlled master cylinder on saiddriven vehicle, said auxiliary master cylinder will transmit fluid underpressure to the brakes of the hydraulic braking system of the towedvehicle to simultaneously engage the brakes on the towed vehicle and thebrakes on the driven vehicle.
 2. A hydraulic braking system for a drivenvehicle and a towed vehicle, which vehicles are mechanically coupled formovement over the terrain, under the power of the driven vehicle, asdefined in claim 1; wherein a. said hydraulic conduit which is connectedin fluid communication with the conduit system leading to the respectivebrakes of the driven vehicle, is a flexible conduit.
 2. selectivelycontrolable valve means intermediate said auxiliary master hydraulicpower cylinder and said conduit system leading to said second hydraulicpower actuated cylinder-plunger assembly, g. selectively controllablevalve means intermediate said second master hydraulic power cylinder andsaid second conduit system leading to said second hydraulic poweractuated cylinder-plunger assembly, h. said plunger extending from saidfirst hydraulic power actuated cylinder-plunger assembly and beingconnected, in power transmitting relation with said auxiliary masterhydraulic power cylinder, so upon actuation of said first masterhydraulic power cylinder, said plunger of said first hydraulic poweractuated cylinder will actuate said auxiliary master hydraulic powercylinder, which, in turn, will actuate said second hydraulic poweractuated cylinder, i. said first power actuated cylinder being separablewith respect to said auxiliary master hydraulic power cylinder so noloss of hydraulic fluid will be had when the two systems are separated,and j. fastening means detachably connecting said first hydraulic poweractuated cylinder-plunger assembly with said auxiliary master hydraulicpower cylinder to transmit lineal force to said auxiliary masterhydraulic power cylinder.
 2. a valve within said conduit whichinterconnects said auxiliary master cylinder with the hydraulic brakingsystem of the towed vehicle, d. a hydraulic conduit connected in fluidcommunication with the conduit system leading to the respective brakesof the driven vehicle,
 3. A hydraulic braking system for a drivenvehicle and a towed vehicle, which vehicles are mechanically coupled formovement over the terrain, as defined in claim 2; wherein a. saidcylinder-plunger assembly connected to said flexible conduit isconnected in axial alignment with the piston of said auxiliary mastercylinder.
 4. A hydraulic braking system for a driven vehicle and a towedvehicle, which vehicles are coupled for movement over the terrain; asdefined in claim 3, wherein a. fastening means detachably secure saidcylinder-plunger assembly to said auxiliary master cylinder.
 5. Ahydraulic braking system for a driven vehicle and a towed vehicle, whichvehicles are mechanically coupled for movement over the terrain underthe power of the driven vehicle, as defined in claim 1; wherein a. saidvalve means interposed between said master cylinder on the towed vehicleand the conduit system leading to the respective brakes thereof isadapted to be selectively closed, and b. said valve within said conduitwhich interconnects said auxiliary master cylinder and the hydraulicbraking system of the towed vehicle is adapted to be opened to renderthe hydraulic braking system of the towed vehicle simultaneouslyoperable with the braking system of the driven vehicle.
 6. A hydraulicbraking system for a driven vehicle and a towed vehicle, which vehiclesare mechanically coupled for movement over the terrain under the powerof the driven vehicle, as defined in claim 1; wherein a. saidcylinder-plunger assembly having the piston fitted therein in fluidtight relation,
 7. An apparatus embodying two hydraulic systems, whichsystems are adapted to be mechanically connected so one of the systemsis synchronously operated by the other of said systems without thehydraulic fluid from one system passing into the other of the hydraulicsystems, which apparatus comprises; a. a first master hydraulic powercylinder, b. a first conduit system connected in fluid communicationwith said first master hydraulic power cylinder and leading therefrom,c. a first hydraulic power actuated cylinder-plunger assemblyoperatively connected in fluid communication with said first conduitsystem, d. a second master hydraulic power cylinder,
 8. An apparatusembodying two hydraulic systems, as defined in claim 7, wherein a. saidsecond hydraulic system has a plurality of cylinder-plunger assembliesoperatively connected in fluid communication with said second conduitsystem.